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Exploring Coral Sustainability with New Technologies

The Island of Bonaire in the Southwest Caribbean, a Marine Protected Areas since 1979, has one of the most pristine coral reefs in the Mark Patterson, region. The last synoptic survey of Virginia Institute of Marine Science (VA, the leeward coast was by the Dutch USA) scientist Dr. Fleur van Duyl in the 1980s and parts of the deeper reef have never been mapped. In January Figure 1: Bathymetric Site Map of Bonaire, Netherlands Antilles. Contours are in intervals of X m. Thumbtack markers indicate locations of AUV operation. 2008, the US National Oceanographic and Atmospheric Administration The crystal clear waters learn about and engage in cutting- and schools of reef fish made an edge oceanographic exploration. Tom Hilller , (NOAA) funded a unique expedition to enchanting setting for the first geoacoustics (UK) Bonaire, deploying 3 compact NOAA Ocean Explorer Signature At a recent meeting of the Interna- Exploration Expedition of 2008. An tional Initiative (ICRI), Autonomous Underwater Vehicles international team of scientists and delegates identified mapping the (AUVs) carrying various engineers from academia, reefs of Bonaire as a top priority. government, and industry gathered Bonaire’s reefs are unique in a oceanographic instrumentation on Bonaire in the Netherlands regional context and in 2004 were packages and a swath bathymetry Antilles, a 35 km long island about 90 proposed for United Nations World km north of Venezuela (12º10’N Heritage Status. In this context the . 68º15’W) (Figure 1- Nautical Site NOAA expedition Bonaire 2008: Map of Bonaire). Their mission was Exploring Coral Reef Sustainability to use new technology to look at the with New Technologies was coral reefs and ocean environment proposed by Mark Patterson of the around the island. Accompanying Virginia Institute of Marine Science them were 16 undergraduate (VIMS), along with co-Principal students from the University of Investigators Arthur Trembanis Delaware, participating in a new (University of Delaware), and Jim science study abroad program to Leichter and Dale Stokes (Scripps Institution of ). The goals of the expedition were to: • Produce comprehensive maps of the sea bottom environment of Bonaire over a substantial depth range (i.e. shore to twilight zone); • Describe physical and chemical conditions near healthy bottom ecosystems (e.g. currents, temper- ature, and dissolved levels); Figure 2: A) Preparing to launch the UBC Gavia from platform of the D/V Green Flash. and Nukove Bonaire. B) Fetch1 AUV in the background while VIMS graduate fellow Noelle Relles conducts a visual survey • Investigate biodiversity of “deep” of the reef (twilight zone and beyond) bottom Images courtesy of Bonaire 2008: Exploring Coral Reef Sustainability with New Technologies. ecosystems, with particular

14 | September 2008 | Hydro international Figure 3: A) Fetch1 AUV gliding over a dense shallow water field of Elkhorn coral (Acropora palmata) B) Gavia AUV (Hafmynd ehf) with GeoSwath bathy sonar module preparing to set off on a reef survey mission. Images courtesy of Bonaire 2008: Exploring Coral Reef Sustainability with New Technologies.

attention to new types of commu- During the first full week of January Fetch1 AUV was developed by Mark nities and new invertebrate dive locations and AUV launch sites Patterson and Jim Sias (described in species. were scouted and the rest of the Hydro International, October 1998, team arrived, including the 16 Turn-Key Autonomous Underwater The Bonaire reefs have largely undergraduate students from the Vehicles: A New Option for Seabed escaped the recent coral reef crisis University of Delaware. Next, the Exploration and Imaging) and seen worldwide. A 2005 survey of the three AUVs were assembled and carried sensors to measure dissolved state of Bonaire’s reefs by Steneck tested and diving operations using oxygen, pH, CTD, underwater video and McClanahan (2005) found that SCUBA were started (Figure camera, and high frequency side- they were among the healthiest reefs 2). scan sonar. Hafmynd ehf, a company in the Caribbean. This makes based in Iceland, developed the Bonaire’s reefs uniquely important TheA utonomous Underwater Gavia AUV. As well as the standard as baselines for comparison with Vehicles (AUVs) were the techno- range of sensors (e.g. , GPS, other Caribbean coral reef logical centerpiece of the Bonaire altimeter, camera) each Gavia ecosystems. Detailed mapping of 2008 Expedition (Figure 3). Two carried a special payload: the Gavia Bonaire’s shallow- and deep-water kinds of small AUVs were used, one from the University of British coral reefs is a top priority for Fetch1 vehicle (Figure 3A) and two Columbia carried a sensitive CTD protecting these ecosystems, as well Gavia AUVs (Figure 3B) each with while the other Gavia carried a as for defining a baseline for investi- slightly different but complimentary GeoSwath wide swath bathymetric gating and possibly restoring other payload sensor configurations. The sonar from GeoAcoustics Ltd. The Table 1 coral reef systems. The expedition’s findings will also help the Island Government of Bonaire continue to AUV Fetch 1 Gavia-UBC Gavia-Hafmynd protect this unique ecosystem and manage their marine reserves. Length/ 2 m / 70 kg 2.4 / 55 kg 2.7 m / 78 kg Depth rating 300 m 500 m 250 m Advance teams from the Virginia Endurance/batteries 4 hrs / Lead-acid 6 hrs / Lithium-ion 6 hrs / Lithium-ion Institute of Marine Science and Side-scan sonar Marine Sonic 600 kHz Imagenex 220/990 kHz Marine Sonic 900/1800 kHz University of Delaware arrived in Bathymetry Sonar None None GeoSwath-Plus 500 kHz Bonaire at the end of December 2007 to meet with local government CTD; Up/down ADCP; INS; DVL; camera/strobe; sound officials and start the process of Other payloads pH; Oxygen; CTD; video DVL; camera/strobe; velocity sensor optical sensor; acoustic mobilizing the infrastructure and modem equipment required for the project.

Hydro international | September 2008 | 15 Figure 4: A) The deeper end of a Gavia survey pattern to the south of Klein Bonaire, showing the vehicle run-lines (in blue) and GeoSwath sonar bathymetry. The survey was run at 15 m fly height with 30 m & 60 m line spacing (see text). Depths shown in this image are from 150 m to 250 m and no vertical exageration has been applied. Note the sonar swath extending from above the vehicle due to the steep slope. B) The bathymetric sonar onboard the Gavia AUV provides an incredibly dense map of the reef structure. Each colored dot represents a sonar depth measurement with the colors indicating depth (dark blues are shallow < 5 m and yellows are depths around 35 m). Black areas are shadow zones where the reef drops off steeply. You can see the overhanging coral on the crest of the reef and the steep sheer face, which is why this dive site is called “Cliffs”. Each AUV mapping survey generates millions of bathymetric soundings. Images courtesy of Bonaire 2008: Exploring Coral Reef Sustainability with New Technologies.

Gavia is one of the smallest AUVs several beach-launch and boat- SCUBA divers using underwater capable of carrying such a wide launch missions where all three video, and hand-held instruments. range of sensors. AUVs were simultaneously The VIMS team used a diver- collecting data in the same area. deployed profiling instrument that A typical operational day saw the used the same sensors carried by the three AUVs in the water (Figure 4) Because AUVs can fly through the Fetch1 AUV. early in the morning until lunch then water column or in close proximity a break for battery recharge and data to the bottom (in terrain-following The GeoSwath payload unit was built download, and transit to a new mode) they provided a superior by GeoAcoustics Ltd of Great survey site for an afternoon mission. method of carrying sensitive sensors Yarmouth (UK), and is a minia- The Fetch1A UV (Figure 3B and right to the survey site compared to turised version of the popular Figure 4A) ran linear transects from using a surface boat (Figure 4). boat-mounted GeoSwath Plus inter- shallow to deep water at many of Dr. Operating up to 220 m deep the ferometric sonar. The GeoSwath van Duyl’s sites surveyed in the 1980s Gavia AUV with the GeoSwath flew sonar uses sound to remotely sense but this time in place of aerial photos survey patterns at a constant 15 m the properties of the seafloor. It and spot SCUBA dives the team altitude to collected high-resolution sends out a ping of sound more than utilized high frequency side scan 500 kHz simultaneous side-scan and 15 times per second. This sound sonar (600 kHz), underwater video, bathymetry data. Both the Fetch1 scatters (echoes) from the sand, and water quality sensors (i.e. vehicle and the UBC Gavia carried coral, and rocks that it hits and the Oxygen, CTD). The two GaviaA UVs side-scan sonar systems (see Table GeoSwath uses these echoes to (Figure 3A and Figure 4B) ran 1). The UBC Gavia also measured measure the range to the seafloor lawnmower patterns at select water currents near the bottom, and its acoustic scattering locations along the leeward side of chlorophyll, conductivity, and properties. From one ping the Bonaire and Klein Bonaire, including while the Fetch1 vehicle GeoSwath can measure a line of up sites of special interest to the terri- measured dissolved oxygen, pH, to 5000 points extending 40 meters torial government of Bonaire. conductivity, and temperature. The or more to either side of the AUV Multiple missions were completed expedition team also deployed fixed (Figure 5). As the AUV swims over from various beaches and jetties bottom instruments to measure the reef at about 4 knots (2 m/s) the around the island, with both temperature fluctuations and water GeoSwath is continually mapping shoreline missions and deep dive currents. The robot mapping effort what lies beneath. After each survey missions down to beyond the 200 m was ground-truthed at selected was complete the AUV returned to depth contour. Operations included spots by compressed air and trimix the beach and the data was

16 | September 2008 | Hydro international Figure 5: Bathymetric charts overlaid on top of a satellite photo of the island. Collecting sonar Figure 6: 500 kHz digital side-scan sonar mosaic created from survey data collected by the data in the field is only the step of post-processing the data aimed at producing bathymetry GeoSwath sonar on the Gavia AUV. Bright areas indicate high backscatter return energy charts. Each rectangular shaped patch represents a single survey mission lasting between 1 - associated with coral fragments or scattered rocks while dark patches represent shadow 2 hours of robot swim time. Colors indicate depths from shallow (dark blue) to depths of 170- zones or patches of soft sand and/or mud that absorb more sound than rocks or corals. In 180 m below the surface (red). The thick and thin black lines represent isobath contours. this image the beach is towards the right and each grid cell is a 10 m x 10 m square. The Charts like this helped to identify target areas for deep trimix diving and helped the marine total swath width is 40 m (in less than 5 m of water) and the line length from tip to tip is park managers inventory the shallow and deep reef areas of Bonaire. approximately 100 m. Image courtesy of Bonaire 2008: Exploring Coral Reef Sustainability Image courtesy of Bonaire 2008: Exploring Coral Reef Sustainability with New Technologies. with New Technologies.

downloaded to the processing (DVL), gave a position error with less especially interested in investigating computer. In the case of the than 0.5 m drift per hour, so the these processes at several locations GeoSwath-enabled Gavia the data missions were kept fairly short where there is some concern about was used to make the depth (typically 2-3 hours) to ensure that the effects of land development. The (bathymetry) and scattering high-resolution binning could be sand-filled grooves between coral intensity (side-scan) maps of the used. spur formations, and the sand plains survey area. One of the key features of the in deeper water are also of interest. GeoSwath is that it collects simulta- Understanding sediment movement The Gavia carrying the GeoSwath neous true digital side-scan data can help predict whether an ancient sonar alone ran a total of 40 km of with the bathymetry. The side-scan shipwreck, or a modern-day mine, trackline survey over 8 days of resolution of the 500 kHz system is might be visible on the seafloor. The missions. TheA UV surveyed from 0.5 degree along track and 3 cm effects of currents and waves on the the beach to 220 m deep, which is the across track, giving highly detailed appearance of the seafloor in and maximum depth rating of this model images of the sea floor, corals and around coral reefs is not well known of Gavia (a 1000 m version is also even the fish in the water column and is one of the focus areas of this available). The maximum bottom (Figure 7). The backscatter data was research project. depth seen was over 250 m. also effective in mapping and classi- Typically the missions were run at 15 fying the seafloor bottom type over Finally, in cooperation with the US m terrain following height with the the survey area, and the resulting Geological Survey (USGS), the AUVs GeoSwath sonar set to achieve 70 m classification was matched to diver were used to map geological features swath width. The surveys were run ground-truthing. and find evidence of how Bonaire using the ‘side-scan search pattern’ fared during a suggested series of with parallel lines up to 1.2 km long Coral reefs have interesting geology tsunamis that may have struck the spaced at 30 m & 60 m – this ensured as well as biology. Sediment island about 4,000 years ago. The that every object ensonified had a movement and location are USGS wants to understand how past side scan shadow in at least one line important to measure around coral tsunamis affected low-lying areas (Figure 6). Typically the GeoSwath reefs. Land-use practices onshore and islands so they can better assess data was inspected as scrolling can affect sediment distribution and tsunami risks. The ability of waterfalls and processed to a 0.5 m abundance on the reef, and many the AUVs to gather high-resolution, grid: the Kearfott T24 inertial reef organisms can be harmed if precisely located bathymetry and navigation system (INS), when aided there is too much sediment present. backscatter data from the shore by the RDI Doppler velocity log The government of Bonaire is down to several hundred meters is a

Hydro international | September 2008 | 17 Table 2 Date Start (UTC) End (UTC) No. of lines Line length Max depth Notes Extracts from the Survey log of one 12th Jan 13:00 14:00 4 lines 00 m 80 m Jetty launch / beach recovery of the Gavia AUVs: 8 days of 15:00 15:40 7 lines 500 m 90 m Jetty launch at Dive & Adventure GeoSwath survey 21:50 23:10 4 lines 250 m 30 m Beach launch at science camp missions. 13th Jan 14:00 16:00 8 lines 350 m 30 m Pink Beach - beach launch 23:20 00:10 4 lines 400 m 1 m Very shallow survey 2m-10m near science camp 14th Jan 14:40 15:20 1 line 1200 m 160 m From science camp across channel to Klein Bonaire 23:50 01:12 4 lines 280 m 5 m 15th Jan 18:30 19:00 4 lines 500 m 50 m 19:50 20:30 1 line 600 m 150 m A single cross-line 16th Jan 16:10 17:00 8 lines 550 m 220 m Klein Bonaire, beach to max depth 17th Jan 15:20 17:30 11 lines 350 m 220 m New Cove, beach to max depth 18th Jan 15:00 15:50 6 lines 500 m 195 m National park, beach to deep 16:40 16:50 1 line 200 m 80 m 19th Jan 15:10 15:50 8 lines 400 m 200 m Klein Bonaire (boat launch) 17:00 19:00 6 lines 1050 m 180 m Longer survey at depth

valuable asset in the investigation of Bonaire 2008: The Explorers The full list of the Bonaire 2008 tsunami impacts. Mark Patterson of the Virginia ‘explorers’ can be found on the Institute of Marine Science (VIMS) expedition website (81) Many gigabytes of environmental led the Bonaire 2008 Expedition, and seabed mapping data were along with co-Principal Investi- The Authors collected for analysis and publi- gators Arthur Trembanis of the cation in the scientific journals over University of Delaware, with Jim Art Trembanis B.S. Geology, (Duke University) the coming months. After the Leichter and Dale Stokes from and Ph.D. Marine Science (College of William and success of this mission future AUV Scripps Institution of Oceanog- Mary) is Assistant Professor of Geological Sciences and Director of the Coastal Sediments, expeditions to Bonaire are already raphy. Scientists also assisted the Hydrodynamics, and Engineering Laboratory being planned. This will include mission from NOAA’s Undersea (CSHEL) at the University of Delaware. His surveys of the windward side of the Research Center (Otto Rutten), the research interests are in the measuring and modeling of coastal morphodynamics particularly Island, where it is too dangerous to University of British Columbia beach erosion, beach nourishment, bedform take small dive boats. This (Bernard Laval and Alex Forrest), behavior, and scour processes associated with expedition was a great example of Northeastern University (Sal seafloor objects including shipwrecks and mines. the unique abilities of small AUVs Genovese), and the National * [email protected]

such as the Fetch and Gavia to carry Oceanography Centre Southampton Mark Patterson, AB magna cum laude, AM, PhD high-resolution sonar payloads like (Ken Collins, Jenny Mallinson). The Biology (Harvard), is Associate Professor of Marine the GeoSwath into areas where other Island Government of Bonaire, the Science, NOAA , and Director of the survey technologies cannot reach. Bonaire Marine Park Authority Autonomous Systems Laboratory, Virginia Institute of Marine Science. He is lead inventor on US TheC oastal Sediment Hydrody- (special thanks go to Ramon de Patents 5995882 (AUVs) and 7221621 (neural namics and Engineering Lab at the Leon, the Marine Park Manager) network target recognition). From 1996-2005, he University of Delaware has now and STINAPA, a management was co-founder and VP of Sias Patterson, an AUV taken delivery of a Gavia AUV with a advisory body, provided local maker, where he helped design the Fetch- and NNemo-class AUVs. GeoSwath sonar and is working support to the project. Technology * [email protected] together with researchers at the specialists from Iceland (Richard Center for Coastal and Ocean Yeo and Eggert J. Magnússon from Tom Hiller received his BSc and PhD degrees in Mapping at the University of New Hafmynd Ehf) and England (Tom Physics from Bristol University, UK. Dr Hiller has worked in application engineering and product Hampshire to develop new Hiller and James Baxter from management for several UK sonar manufacturers techniques for bathymetric sonar GeoAcoustics Ltd) helped run the as well as for his own company, Anka Ltd. At data interpretation. VIMS survey equipment. On hand to help GeoAcoustics Ltd he has been involved in the researchers are exploring neural with the AUV deployment, data development of a range of new technologies, including the GeoSwath interferometric multibeam, network algorithms to classify water collection and, most importantly, to digital side-scan , synthetic aperture sonar column targets like fishes and jellies learn from the unique collection of and 3D sub-bottom imaging systems. from side-scan sonar to enhance the expertise present were 16 students * [email protected] value of these unique datasets (US from the 2008 Study Abroad Patent 7221621). Seafloor mapping Program of the University of and ecosystem analysis can now Delaware. 81. http://oceanexplorer.noaa.gov/ occur simultaneously when AUVs explorations/08bonaire/ are utilized.

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